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Physics {Electricity Part I Summer} π· - Coggle Diagram
Physics {Electricity Part I Summer} π·
Formulas
voltage = current x resistance (V=IR)
charge = current x time (Q= It)
energy transferred = current x voltage x time (E= I x V x t)
power = current x voltage (P=IV)
energy transferred = charge x velocity (E= QV)
Units
coulomb (C) - unit of energy transfer
joule (J) - unit of energy
ampere (A) - measures current
ohm (Ξ©) - measures resistance in circuit
volt (V) (J/C) - measures voltage (potential difference)
watt (W) - measures power
Safety Features of Mains Electricity
insulation
-cover copper wires with insulating material to prevent electrocution
double insulation
- around wires, non-metallic case
circuit breakers
- an automatic electromagnet switch that can switch off electricity in the house, it doesn't melt/break so it can be reset and doesn't need to be replaced.
earthing
- the earth wire provides a low resistance path to the earth if there is extra current when the live wire touches the metal casing, the current passes into the earth wire a high current to the fuse causes it to melt and break, cutting of electricity to the appliance
fuses
- a glass cylinder containing a thin metal wire that heats up and melts breaking the circuit when current in the wire becomes too large.
Alternating Current vs. Direct Current
Alternatng Current
produced by electrical generators (mains)
has two identical terminals
constantly changing direction
Direct Current
produced by cells and batteries
has a positive and negative terminal
continuous and in one direction
Series Circuit vs. Parallel Circuit
Series Circuit
all current in closed loop in the same A1 = A2 = A3
voltage is divided equally throughout circuit. sum of voltage in components= supply of voltage Vt= V1 + V2 + V3
total resistance = sum of resistance Rt = R1 + R2 + R3
Parallel Circuit
current is split into different branches At = A1 + A2 + A3
all voltage in a parallel circuit is the same across the components, VT = V1 = V2= V3
net resistance decreases as more components are added because there are more paths for current to pass through
RT = 1/R1 + 1/R2 + 1/R3
Components of a Circuit
LEDs
(light emitting diodes) - only allow current to pass in one direction and will illuminate when current flows
LDRs
(light dependant resistors) - as light intensity increases, LDRs resistance decreases.
Diode
- forward bias - current only flows in one direction reverse bias- no current flows in other direction
Thermistors
- as temperature increases, the resistance in the thermistor decreases
the more components in a circuit, the higher the resistance
Filament Lamps
- as resistance increases, temperature increases, atoms vibrate faster, which increases resistance making it harder for electrons to pass through so the current goes slower
Resistors
- as current increases, voltage increases (directly proportional) straight line through the origin
Wires
- as current increases, voltage increases (directly proportional) straight line through the origin
Electric Current
in solid metallic conductors, electric current is a flow of negatively charged electrons
voltage is the energy transferred per unit change passes measured in joules per coulomb(J/C)
current is the rate of flow of charge
current and charge is conserved at junctions of a circuit because electrons cannot be created or destroyed
increasing voltage, increases current, increasing resistance, decreases current
Hazards
Damaged Insulation β
if someone touches an exposed piece of wire, they could be subjected to a lethal shock
Overheating of cables β
passing too much current through too small a wire (or leaving a long length of wire tightly coiled) can lead to the wire overheating. This could cause a fire or melt the insulations, exposing live wires
Damp conditions β
if moisture comes into contact with live wires, the moisture could conduct electricity either causing a short circuit within a device (which could cause a fire) or posing an electrocution risk
Metal Casing
heaters, microwaves could become live and cause electric shocks, fires and explosions
Resistance
Resistance causes transfer of electrical energy to heat energy. Some components are designed to have a high resistance to make sure this happens, for example electrical heaters that have lots of resistors to ensure a high resistance so a lot of heat is produced.
Resistors come in two forms (fixed and variable)
Fixed Resistor
resistance stays constant
Variable Resistors
change resistance depending on length of wire- a longer wire has more resistance than a short one
Circuit Components
An ammeter - to measure the current through the component
A voltmeter - to measure the voltage across the component
A variable resistor - to vary the current through the circuit
Power source - to provide a source of potential difference (voltage)
Wires - to connect the components together in a circuit
